What is "flat called"

Usage examples of "flat called".

Erected on a low, reedy mud flat called Mud Island a few miles below Philadelphia, the fort was surrounded by dikes and fortified with batteries that, wrote a defender, were nothing more than old spars and timber laid up in parallel lines and filled between with mud and dirt.

Erected on a low, reedy mud flat called Mud Island a few miles below Philadelphia, the fort was surrounded by dikes and fortified with batteries that, wrote a defender, “.